2989 - Comparing Cardiac Radiation Dose between Accelerated Partial Breast Irradiation and Whole Breast in Patients Treated with Adjuvant Radiation for Early-Stage Left-Sided Breast Cancer

Purpose/Objective(s):

Standard of care for early-stage breast cancer following breast conserving surgery includes whole breast irradiation (WBI). More recently, accelerated partial breast irradiation (APBI) has become a popular option for patients due to its shorter treatment regimen, lower cost, and increased patient compliance. APBI has shown equivalent ipsilateral tumor recurrence rates and overall survival to WBI. In patients with left-sided breast cancer treated with whole breast irradiation, long term cardiotoxicity is a concern. Early APBI techniques have shown favorable dosimetry compared to WBI for reducing cardiotoxicity. To the best of our knowledge, no study has evaluated cardiac dosimetry for patients treated with the contemporary University of Florence regimen (30Gy in 5 fractions intensity modulated radiation therapy (IMRT)). We hypothesize the APBI-IMRT-Florence regimen to be superior to WBI for reducing heart and left anterior descending coronary artery (LAD) dose.

Materials/Methods:

This was an IRB-approved single institution retrospective dosimetric analysis of patients with left-sided breast cancer who underwent breast conservation therapy and treated with either whole breast radiation or the APBI-IMRT-Florence regimen at our institution between 2022-2024. This dosimetric study evaluated mean and max dose to the heart and LAD. Patients were stratified by use of breath-hold technique. Statistical analysis was performed using R (version 4.4.0).

Results:

Of the 84 patients included in the study, 63 underwent WBI and 21 underwent APBI. 52 patients and 12 patients who underwent WBI and APBI, respectively, were treated with breath-hold. Table 1 summarizes the dosimetric findings. APBI had significantly less (p<0.001) mean and max doses for both the heart and LAD compared to WBI. These differences were maintained independent of breath-hold.

Conclusion:

This study provides evidence supporting the APBI-IMRT-Florence regimen for reducing cardiotoxicity. Even when utilizing respiratory management, the benefits of APBI were upheld. This short, convenient regimen may provide superior cardiac outcomes while also reducing barriers to care. Further studies are needed to evaluate potential confounders such as lumpectomy location and volume and to assess biologically effective dose and volumetric dosimetry.

Abstract 2989 - Table 1

	WBI (N=63)	APBI (N=21)	p-value
Heart Mean (Gy)	0.966	0.252	<0.001
Heart Max (Gy)	15.3	2.02	<0.001
LAD Mean (Gy)	2.84	0.671	<0.001
LAD Max (Gy)	6.97	1.24	<0.001